(a) Field of the Invention
The present invention relates to a rechargeable lithium battery and a method of fabricating the same.
(b) Description of the Related Art
The demand for rechargeable lithium batteries having a high energy density is increasing as the use of portable electronic instruments such as portable phones, camcorders, and notebook computers is increasing. Particularly, when a negative electrode has low potential on charging a battery, it tends to decompose the electrolyte, so that battery performance factors such as capacity, capacity retention, cycle-life characteristics, and low temperature performance deteriorate. Accordingly, it is important to prevent the negative electrode from reacting with the electrolyte in order to improve battery performance in a rechargeable lithium battery having an electrolytic organic solution or a polymer electrolyte.
Reactivity with the negative electrode should be considered when choosing a material for an electrolyte. Many solvents and mixtures for the electrolyte have been proposed to be non-reactive with the negative electrode. In addition to non-reactivity, solubility of supporting salt, reactivity with the positive electrode, ion-conductivity, and cost are considered when choosing the solvent for an electrolyte.
Examples of non-aqueous solvents for a rechargeable lithium battery that have been proposed include ethylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, γ-butyrolactone, methyl propionic acid, butyl propionic acid, ethyl propionic acid, and mixtures thereof.
Another approach that has been attempted is inhibiting the reaction between the negative electrode and the electrolyte by adding a certain compound to the electrolyte, so that the battery performance improves. However, the compound adversely affects the charge and discharge reaction, and it is hard to provide the desired voltage and current in the battery.
Japanese Patent Laid-open Publication No. 1996-96852 discloses a battery including a negative electrode having a material for doping and dedoping lithium or metallic lithium, in which a non-aqueous solvent is composed of vinylene carbonate. It is not expected to improve the battery performance in a battery having a negative electrode of carbonaceous material, however, since the vinylene carbonate insufficiently coats the negative electrode.
When vinylene carbonate is added, excessive gas is generated and the battery deforms. It is believed that the gas generation is caused by the decomposition of electrolyte during formation of the coating layer at the first charge. The electrolyte is thereby denatured by the gas generation, resulting in impairment of the battery performance.